Electronic timepieces with an electricity-generating unit that converts external energy such as optical or mechanical energy to electric energy to utilize the electronic energy for driving an electronic device have been proposed.
Examples of an electronic timepiece with such electricity-generating unit are a mechanically electricity-generating type timepiece that converts mechanical energy of a rotary weight to electric energy to utilize the same, a temperature-difference electricity-generating type timepiece that generates electric power by serializing a plurality of thermocouples to utilize temperature differences between both ends of the thermocouples, and a solar-battery type timepiece that utilizes a solar battery.
As the electronic timepiece using a solar battery as the electricity-generating unit, an electronic timepiece using a solar battery with a one-stage cell constitution has been proposed (for example, see Japanese Patent Application Laid-open No. H9-96686, pages 5 to 7 and FIG. 1). As compared with a conventional solar battery having a four-stage cell constitution, the solar battery having the one-stage cell constitution has excellent appearance and has excellent efficiency on an effective light receiving area, because a light receiving face thereof does not include any splitting slit. Therefore, the solar battery having the one-stage cell constitution is expected to be an electricity-generating unit for an electronic timepiece.
As an electronic timepiece with such electricity-generating unit, an electronic timepiece provided with a power-source peripheral circuit that boosts an electricity generation output from an electricity-generating unit by using a boosting unit and stores the same has been proposed. FIG. 23 is a block diagram of an electronic timepiece 2300 proposed. In the conventional electronic timepiece 2300, a current path is formed of an electricity-generating unit 2301, a charging diode 2306, and a timing unit 2304.
The timing unit 2304 is a timepiece block that displays clock time by utilizing electric energy. An output of the electricity-generating unit 2301 can be boosted via a boosting unit 2302 to charge a storage unit 2303.
In the electronic timepiece 2300, when the storage unit 2303 is discharged to be approximately empty and the electricity-generating unit 2301 is not generating electric power, the timing unit 2304 stops its operation. Thereafter, when the electricity-generating unit 2301 starts to generate electricity, generated energy is first fed to the timing unit 2304 and a boosting control unit 2305.
When a generated voltage in the electricity-generating unit 2301 reaches a level sufficient for actuating the timing unit 2304 (for example, 1.0 voltage) or higher, the timing unit 2304 starts re-actuation behavior. A frequency-divided clock signal Sx is outputted from the timing unit 2304 and a signal (Sy in FIG. 23) obtained by further frequency-dividing the signal Sx is fed from the boosting control unit 2305 to the boosting unit 2302. As a result, the boosting unit 2302 starts a boosting behavior.
When the timing unit 2304 once starts a behavior, even if the generated voltage from the electricity-generating unit 2301 slightly lowers, an timing behavior of the timing unit 2304 is maintained and the storage unit 2303 can be charged up to a high voltage, because the generated output is boosted by the boosting unit 2302 and fed to the timing unit 2304.
However, in an electronic timepiece provided with the power-source peripheral circuit, an open voltage corresponding to one stage in a solar battery used as an electricity-generating unit is just under about 0.7 voltage even under a high illumination density. On the other hand, a crystal oscillation circuit ordinarily used for the conventional electronic timepiece 2300 shown in FIG. 23 requires at lowest about 0.6 voltage to 0.8 voltage for oscillation actuation.
Accordingly, when a solar battery having a one-stage cell constitution is intended to be utilized as the electricity-generating unit 2301, a voltage drop larger than at least 0.1 voltage occurs in the charging diode 2306. Thereby, since a margin of an oscillation starting voltage in the crystal oscillation circuit to a voltage applied to the crystal oscillation circuit itself in the timing unit 2304 is completely lost, the voltage applied becomes lower than the oscillation starting voltage in the crystal oscillation circuit. As a result, there is a problem that the crystal oscillation circuit can not start.
Particularly, since an electronic timepiece for a woman is smaller than an electronic timepiece for a man, it must use a solar battery with a small effective light-receiving area, so that the above problem becomes significant. Therefore, there is another problem that the crystal oscillation circuit can not be installed in the electronic timepiece for a woman.
Currently, an electronic timepiece where a solar battery that has a one-stage cell constitution similarly and is formed in a ring shape is used and the solar battery is attached at a peripheral edge of a timepiece dial is put in a practical use. However, since a light-receiving area in the solar battery can not be enlarged due to a structure of a timepiece, it is necessary to receive not only direct light but also light reflected from the timepiece dial. Accordingly, since only a white-base color, which reflects light, can be adopted for the timepiece dial, there is such a problem that the timepiece dial is restricted regarding its design.
The present invention has been made in view of these problems, and an object thereof is to provide an electronic timepiece and an electronic device that can be reduced in size by performing reliable actuation of the electronic timepiece and the electronic device with a voltage lower than a voltage required for actuation, and an actuating method. Further, another object of the present invention is to provide an electronic timepiece and an electronic device that can achieve improvement of decorative performance including a color of the electronic timepiece or the electronic device, and an actuating method.